The cathedral, of the 12th century, has a carved portal and three apses decorated with small arches and pilasters, and contains a fine pulpit and episcopal throne in marble mosaic. Near it are two grottos 1 To the period after 335 belong numerous silver and bronze coins with the legend Caleno.
Pietro Orseolo and his successors rebuilt the church on a larger scale in the form of a basilica with three eastern apses and no transept, and Byzantine workmen were employed.
The eastern crypt, or confessio, extends under the whole of the choir and has three apses, like the upper church.
The cathedral (dedicated to St Nicholas the Pilgrim, a Greek assassinated at Trani in 1094 and canonized by Urban II.), on a raised open site near the sea, was consecrated, before its completion, in 1143; it is a basilica with three apses, a large crypt and a lofty tower, the latter erected in1230-1239by the architect whose name appears on the ambo in the cathedral of Bitonto, Nicolaus Sacerdos.
The cathedral of St Jean, the chief of the numerous churches of the town, was founded in the 4th century but has often undergone reconstruction and restoration; it resembles the Rhenish churches of Germany in the possession of apses at each of its extremities.